Subject: Zoology
Class: 2nd Semester
Comparative Anatomy and Developmental Biology of Vertebrates
UNIT: 1
3.1. Skin Structure
Skin or integument covers body, nasal sacs, openings (gut and urinogenital openings). It has
outer thin epidermis and inner thick dermis. Epidermis is ectodermal in origin and dermis is
mesodermal.
1. Epidermis: It is a stratified epithelium, made up of many layers inner most layer called
stratum germinativum or Malpighian layer outermost layer called stratum corneum or horny
layer.
Innermost layer is made of tall, undifferentiated, actively dividing cells. outermost
layer is made of flat, horny cells and is sloughed off in small pieces or as a whole and
replaced by cells produced from Malphighian layer.
2. Dermis: It is formed of connective tissue containing blood, lymph vessels, nerve fibre,
receptors, smoothmuscle fibers. It is distinguished into two regions: outer region stratum
laxum or spongiosum having loosely arranged connective tissues. Bears branched pigment
cells (chromatophores ).
Inner region stratum compactum have packed connective tissue.
Comparative Anatomy
1. Cyclostomes and fishes: Slimy Skin, outer layers of epidermis show little flattening and
keratinization consequently stratum cornea is lacking. It bears similar cells all through its
thickness. In epidermis are present abundant unicellular mucous glands. Dermis gives rise to
dermal scales is fishes. It bears chromatophores.
Cyclostomes can change skin color to some extent.
2. Amphiba: Thin, Slimy, naked skin. Stratum corneum is heavily keratinized in toads,
moderately in others. Dermis bears chromatophores, vertical and horizontal collagen fibre,
large multicellular mucous and poison glands (more in toads than in frogs), scent glands
(certain tailed forms). Dermis forms minute dermal scales in limbless amphibians.
Change of skin color is common.
3. Reptiles: Thick, dry skin. Stratum corneum heavily keratinized. Forms scales all over and
claws over digit tips. Epidermal scaly exoskeleton is shed periodically as a whole in snakes
,and as fragments in others. Glands are lacking altogether.Dermis contains abundant
chromatophores; forms dermal bony plates in some cases (Tortoise, turtles, crocodiles).
Skin color changes occur in chamaeleons and blood suckers.
4. Birds: thin, dry skin. Stratum corneum is keratinized. It forms feathers, scales and claws
on feet, horny sheath on jaws to form beak.
Glands lacking except oil gland on tail. Pigment confine to feathers. Dermis has abundant
receptors.
5. Mammals: Thick, glandular skin.Stratumcorneum is keratinized. Forms hair, fur, claws,
nails, hoofs at digit tips. Scales in Pangolin, Armadillo and Rat; spines in Hedgehog and
spinny ant eater besides hair, horns in ungulates. Epidermis contains melanophores.
Dermis is rich in receptors and various glands (sweat, sebaciousetc). skincolor not changed.
, INTEGUMENTARY DERIVATIVES
Integumentary derivatives are
Epidermal derivatives
, Glands Exoskeltal structures
i) Scales (Reptiles, few mammals, bird feet)
ii) Feathers – Birds
iii) Hair – Mammals.
iv) Claws – (Reptiles, Birds, Mammals)
Digital tips v) Nails – (Primates among mammals)
vi) Hoofs- (Ungulate Mammals)
vii) Horns – (Mammals)
viii) Beak – Birds.
ii) Dermal derivatives:
Exoskeltal structures Endoskeletal structure
i) Scales (in fishes)
e.g: Membrane bones in skull of vertebrates
framed in dermis sink down and
become Incorporated into endoskelton
Glands
Unicellular Multicellular
Modified epidermal cells Formed by ingrowth
e.g.mucous glands in cyclostomes, of stratum germinaitivum
larval amphibians secreting into dermis.
mucus having a protein substance mucin.
Class: 2nd Semester
Comparative Anatomy and Developmental Biology of Vertebrates
UNIT: 1
3.1. Skin Structure
Skin or integument covers body, nasal sacs, openings (gut and urinogenital openings). It has
outer thin epidermis and inner thick dermis. Epidermis is ectodermal in origin and dermis is
mesodermal.
1. Epidermis: It is a stratified epithelium, made up of many layers inner most layer called
stratum germinativum or Malpighian layer outermost layer called stratum corneum or horny
layer.
Innermost layer is made of tall, undifferentiated, actively dividing cells. outermost
layer is made of flat, horny cells and is sloughed off in small pieces or as a whole and
replaced by cells produced from Malphighian layer.
2. Dermis: It is formed of connective tissue containing blood, lymph vessels, nerve fibre,
receptors, smoothmuscle fibers. It is distinguished into two regions: outer region stratum
laxum or spongiosum having loosely arranged connective tissues. Bears branched pigment
cells (chromatophores ).
Inner region stratum compactum have packed connective tissue.
Comparative Anatomy
1. Cyclostomes and fishes: Slimy Skin, outer layers of epidermis show little flattening and
keratinization consequently stratum cornea is lacking. It bears similar cells all through its
thickness. In epidermis are present abundant unicellular mucous glands. Dermis gives rise to
dermal scales is fishes. It bears chromatophores.
Cyclostomes can change skin color to some extent.
2. Amphiba: Thin, Slimy, naked skin. Stratum corneum is heavily keratinized in toads,
moderately in others. Dermis bears chromatophores, vertical and horizontal collagen fibre,
large multicellular mucous and poison glands (more in toads than in frogs), scent glands
(certain tailed forms). Dermis forms minute dermal scales in limbless amphibians.
Change of skin color is common.
3. Reptiles: Thick, dry skin. Stratum corneum heavily keratinized. Forms scales all over and
claws over digit tips. Epidermal scaly exoskeleton is shed periodically as a whole in snakes
,and as fragments in others. Glands are lacking altogether.Dermis contains abundant
chromatophores; forms dermal bony plates in some cases (Tortoise, turtles, crocodiles).
Skin color changes occur in chamaeleons and blood suckers.
4. Birds: thin, dry skin. Stratum corneum is keratinized. It forms feathers, scales and claws
on feet, horny sheath on jaws to form beak.
Glands lacking except oil gland on tail. Pigment confine to feathers. Dermis has abundant
receptors.
5. Mammals: Thick, glandular skin.Stratumcorneum is keratinized. Forms hair, fur, claws,
nails, hoofs at digit tips. Scales in Pangolin, Armadillo and Rat; spines in Hedgehog and
spinny ant eater besides hair, horns in ungulates. Epidermis contains melanophores.
Dermis is rich in receptors and various glands (sweat, sebaciousetc). skincolor not changed.
, INTEGUMENTARY DERIVATIVES
Integumentary derivatives are
Epidermal derivatives
, Glands Exoskeltal structures
i) Scales (Reptiles, few mammals, bird feet)
ii) Feathers – Birds
iii) Hair – Mammals.
iv) Claws – (Reptiles, Birds, Mammals)
Digital tips v) Nails – (Primates among mammals)
vi) Hoofs- (Ungulate Mammals)
vii) Horns – (Mammals)
viii) Beak – Birds.
ii) Dermal derivatives:
Exoskeltal structures Endoskeletal structure
i) Scales (in fishes)
e.g: Membrane bones in skull of vertebrates
framed in dermis sink down and
become Incorporated into endoskelton
Glands
Unicellular Multicellular
Modified epidermal cells Formed by ingrowth
e.g.mucous glands in cyclostomes, of stratum germinaitivum
larval amphibians secreting into dermis.
mucus having a protein substance mucin.
